Increased performance of many materials is dependent upon a uniform morphology, having a narrow distribution of a morphological properties about a mean morphological value, where the mean morphological value (which may be determined by fabrication parameters) is close to or even equals a characteristic dimension which is by, e.g., a balance between atomic scale parameters and the intended use of the material. Examples include the crystallite sizes and size distribution of, for example, magnetic alloys, and super alloys, and the pore sizes and pore size distributions of heterogeneous catalysts.
The magnetic materials described in our commonly assigned, copending U.S. application Ser. No. 893,516 filed Aug. 6, 1986 of R. Bergeron, et al for Enhanced Remanence Permanent Magnetic Alloy AND Bodies Thereof, and a continuation-in-part thereof also entitled Enhanced Remanence Permanent Magnetic Alloy AND Bodies Thereof filed of even date herewith, both of which are hereby specifically incorporated herein by reference, describe magnetic materials having isotropic magnetic parameters exceeding those predicted by the non-interactive model of the prior art.
As described in the above patent applications, the morphologies necessary for enhanced magnetic parameters include the crystallite grain boundaries being sufficiently free of substantially continuous intergranular phases, and the individual crystallites having dimensions distributed about a material specific characteristic dimension R.sub.o so as to produce a tendency to align the magnetic moments of adjacent crystallites and provide the enhanced magnetic parameters. The material specific characteristic dimension, R.sub.o, is determined by, at least, (i) the interatomic distance of the atoms in the material, (ii) the magnetic exchange field of the material, (iii) the magnetic anisotropy field of the material, and (iv) a material specific scaling factor. The above mentioned properties, i.e., interatomic distance, magnetic exchange field, magnetic anisotropy field and scaling factor, are all material dependent, and there is no one universal value of R.sub.o for all materials. As described in the above referenced patent applications, for the RE.sub.2 Fe.sub.14 B-- type systems, theoretical calculations, with simplifying assumptions, predict a characteristic dimension in the range of 140 Angstroms to 230 Angstroms, with all crystallites having dimensions within a close distribution thereabout, while our observations for materials of the Re.sub.2 Fe.sub.14 B--type confirm that enhanced parameters are observed when the mean crystallite characteristic dimension is within a broader range of 140 to 300 Angstroms, and a major portion of the crystallites have their dimensions closely distributed about the mean.
The actual short range local order of the enhanced magnetic parameter materials is a strong function of the instantaneous and time averaged local cooling rate (temperature change per unit time) and the instantaneous and time averaged thermal flux (energy per unit time per unit area). The solidification and crystallization processes occur with initial cooling rates of 100,000 to 1,000,000 degrees Celsius per second, and average temperature drops (temperature drop while on the chill surface divided by residence time on the chill surface) of 10,000 to 100,000 degrees Celsius per second. These cooling rates drive local instantaneous heat fluxes of hundreds of thousands of calories per square centimeter per second, and average heat fluxes of 10,000 to 100,000 calories per square centimeter per second. Within this cooling rate and heat flux regime, local, short duration upsets, transients, and excursions of the melt pool over the solidifying flakes, splashing of the molten alloy, changes in incoming flow of the molten alloy, formation and passage of alloy-crucible reaction products (slags and oxides) through the crucible orifice, and even bubbles of inert gases as argon entrained under the solidifying flake, and the like, result in a product containing a range of flake and ribbon sizes, crystallite sizes, and crystallite magnetic parameters, ranging from overquenched to underquenched.
A significant problem of early melt spinning trials was the effect of quench transients on the yield, i.e., (1) the final magnetic properties of a major portion of the material, and the (2) fraction of product having magnetic parameters above a threshold value. Prior attempts to control the quench parameters, and especially transients, in order to optimize a property or properties of the quench were generally partially successful, resulting in ribbon product having crystallite dimensions from tens of Angstroms to microns, and a concommitant range of magnetic parameters. This is illustrated in Run 502AB01 of Example IV of Ser. No. 893,516 showing overquenched, underquenched, and near optimum materials in the same melt spun ribbon. By providing a wide range of magnetic parameters that could be correlated with the structural parameters, atmospheric pressure solidification was scientifically very significant. Atmospheric pressure melt spinning allowed synthesis of sufficient material for separation, identification, and characterization of interactive materials of enhanced magnetic parameter material, and especially for comparison and characterization of interactive and non-interactive materials from the same melt spinning run. This is illustrated in Example IV of U.S. application Ser. No. 893,516 . Atmospheric pressure melt spinning resulted in a range of magnetic parameters, including scientifically very significant amounts of magnetic materials that exceeded the Stoner and Wohlfarth limits of (BH)=(M.sub.sat /4).sup.2 and M.sub.rem =(M.sub.sat /2).